1. Field of the Invention
This invention relates to pressure vessels and techniques for storing and dispensing carbon dioxide in the liquid and vapor phase and more particularly, to a carbon dioxide storing and dispensing apparatus and method for storing liquid and gaseous carbon dioxide, for supplying restaurants and other users of the gas. The carbon dioxide storage and dispensing apparatus of this invention is characterized by a horizontal or vertically oriented tank or pressure vessel adapted to receive and store liquid and gaseous carbon dioxide, which vessel is provided with insulation for controlling heat input. A refrigeration system, fill and withdrawal piping, a fill line mixer, volume gauge, heating rod and associated operating and safety control devices are also provided, to complete the system. The carbon dioxide storage and dispensing apparatus is designed to provide a user with an uninterrupted supply of carbon dioxide gas or liquid, while at the same time facilitating storage of larger quantities of carbon dioxide with minimum loss and overcoming other problems associated with presently available equipment and methods.
2. Description of the Prior Art
Current carbon dioxide storage and dispensing systems are characterized by high pressure (800-3000 psig) gas cylinders and low pressure (125-300 psig) liquid cylinders. The high pressure gas system has been in use for many years and has proved to be capable of providing reasonable service with minimum inconvenience to the customer. Replenishment of carbon dioxide in the gas-phase system is accomplished by either switching full cylinders or tanks for empty ones, or filling the end-user cylinders from a delivery vehicle with a high pressure pump under closely controlled conditions. Under circumstances where carbon dioxide is supplied by switching out cylinders, a large inventory of equipment is necessary to service a single customer and high gas losses are experienced by the users, as a result of disconnecting lines and returning partially filled containers to the servicing company. Disconnection also leads to interrupted service, with associated safety and cleanliness problems.
More recently, the use of cryogenic containers (containers fabricated specifically for use at temperatures below -20.degree. F.) have been introduced into carbon dioxide service. These units are preferably stored permanently at the restaurant or other end user location and filled upon demand from a delivery truck, usually by the pressure differential which exists between the container and the delivery unit. This system eliminates the necessity of substituting cylinders, with the accompanying leaks and fluid losses associated with the high pressure cylinder application. However, by nature, the low temperature devices must be designed for very low heat transfer to the stored fluid, in order to minimize pressure build-up and subsequent venting of fluid during low or no-use periods. Accordingly, these systems generally require high performance insulation and a vacuum bottle-type of construction.
The task of filling high pressure carbon dioxide containers, tanks and bottles at a user's site to safe levels and maintaining suitable quantities of carbon dioxide vapor and liquid in the pressure containers at acceptable and safe internal pressures, has resulted in limited storage volume capability for carbon dioxide. Maintaining an acceptable level of container or pressure vessel vacuum over a suitable period of time is difficult and the minimum use rate without gas loss continues to increase beyond a small user's need, under ordinary circumstances. Conversely, the needs of the larger use periods requires the external addition of heat to the container, in order to maintain the minimum required pressure in the system. Pressure-building coils and related controls have been developed to achieve this end, thus introducing further maintenance and operational problems. Other problems such as the difficulty of properly filling a pressure vessel without prior venting to relieve the pressure and wasting carbon dioxide, further underscores the need for improvement.
An object of this invention is to provide a carbon dioxide storage and dispensing apparatus which includes an insulated storage vessel or tank provided with a fill line having a mixer mounted thereon inside the vessel for dispersing incoming liquid carbon dioxide in the vaprous carbon dioxide to achieve rapid vapor-liquid phase equilibrium.
It is another object of this invention to provide a carbon dioxide storage and dispensing apparatus and method for storing both liquid and vaporized carbon dioxide in an insulated pressure vessel to control heat input, using a refrigeration system, fill and withdrawal piping and a fill line mixer located inside the pressure vessel to rapidly achieve equilibrium between the gas and liquid phases.
Another object of the invention is to provide a permanently installed system for storing and dispensing liquid and vaporous carbon dioxide in a wide variety of carbon dioxide usage situations, which system combines wide use range capability with rapid filling capability to the maximum legal gas and liquid volume, without loss or inconvenience to the supplier or user.
Yet another object of the invention is to provide a new and improved carbon dioxide storing and dispensing apparatus which is characterized by an upright or horizontally-mounted insulated pressure vessel fitted with a fill line having a fixed or rotatable fill line mixer mounted inside the pressure vessel, wherein liquid carbon dioxide introduced through the fill line into the pressure vessel impinges upon the mixer to achieve rapid equilibrium between the gas and liquid carbon dioxide phases and minimize the pressure and temperature elevation in the pressure vessel.
Still another object of the invention is to provide a carbon dioxide storage and dispensing apparatus and method for storing and dispensing both gaseous and liquid carbon dioxide, which apparatus includes an insulated pressure vessel provided with a fill line and a fixed or rotatable mixer mounted in the fill line and located in the pressure vessel, in order to rapidly and efficiently mix the liquid and gaseous carbon dioxide, thereby achieving rapid equilibrium between the gaseous phase and liquid phase and minimize losses during filling, as well as achieve optimum pressure conditions inside the pressure vessel.
A further object of the invention is to provide a method for filling a carbon dioxide storage and dispensing apparatus with liquid carbon dioxide in an optimum manner, which includes the steps of introducing liquid carbon dioxide into a pressure vessel, providing a mixing device in the pressure vessel for receiving the liquid carbon dioxide and causing the liquid carbon dioxide to be dispersed in the gaseous carbon dioxide to achieve rapid equilibrium between the gas and liquid phases and maintain equilibrium pressure inside the pressure vessel.